共查询到20条相似文献,搜索用时 31 毫秒
1.
Moti Ram 《Journal of Materials Science: Materials in Electronics》2011,22(8):1081-1084
The Li(Ni7/10Fe3/10)VO4 compound has been synthesized by solution-based chemical route. Its dielectric response is investigated using complex impedance
spectroscopy technique. Frequency dependence of dielectric constant (εr) at different temperatures shows low-frequency dispersion due to polarized structure of the material and mobile charge carriers.
Temperature dependence of εr at different frequencies exhibits the dielectric anomalies in εr at different temperatures. Dielectric relaxation process in the material is signified by the variation of tangent loss with
frequency at different temperatures. The variation of relaxation time with temperature obeys the Vogel–Fulcher law. 相似文献
2.
Moti Ram 《Journal of Materials Science: Materials in Electronics》2012,23(4):936-939
The LiCo3/5Fe1/5Mn1/5VO4 compound was successfully synthesized by solution-based chemical method. The variation of dielectric constant (εr) with frequency at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of εr at different frequencies indicates dielectric anomalies in εr at temperature (Tmax) = 220, 235, 245, 260 and 275 °C with (εr)max ~ 6,830, 2,312, 1,224, 649 and 305 for 10, 50, 100, 200 and 500 kHz, respectively. The variation of tangent loss with frequency
at different temperatures shows the presence of dielectric relaxation in the material. The variation of relaxation time as
a function of temperature follows the Vogel-Fulcher relation. 相似文献
3.
Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using
XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared
samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and
0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease,
and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour
for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature
with increasing frequency. 相似文献
4.
Suhua Fan Fengqing Zhang Guitao Liu Qingbo Tian Luyi Zhu 《Journal of Materials Science: Materials in Electronics》2011,22(12):1778-1782
Bismuth-layered compound Ca0.15Sr1.85Bi4−xNdxTi5O18 (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd3+ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics
increases at beginning then decreases with increasing of Nd3+ doping level, and a maximum Pr value of 9.6 μC/cm2 at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd3+ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (εr) and dielectric loss tangent (tan δ). The magnitudes of εr and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively. 相似文献
5.
The Ln2/3Gd1/3TiNbO6 ceramic compositions are prepared through the solid state ceramic route. The compositions are calcined at 1250 °C and sintered
in the range 1350–1435 °C. Structural analysis of the materials is done using X-ray diffraction analysis and vibrational spectroscopy.
Surface morphology is examined by Scanning Electron Microscopy. Microwave dielectric properties such as dielectric constant
(εr), quality factor (Q) and temperature coefficient of resonant frequency (Tf) are measured using cavity resonator method. The compositions have εr in between 46 and 41.8 and Tf in between +52 and +25 ppm/°C. By the substitution of Gd, the Tf is reduced considerably with a slight decrease in dielectric constant. Cerium based composition had additional reflections
other than that of aeschynite structure. For Pr, Nd and Sm based systems, solid solutions were formed. UV visible spectrum
of the representative composition is recorded and the band gap energy is estimated. Photoluminescence spectra of the samples
are recorded and the transitions causing emissions are identified. The materials are suitable for microwave and optoelectronic
applications. 相似文献
6.
Daojiang Gao K. W. Kwok Dunmin Lin H. L. W. Chan 《Journal of Materials Science》2009,44(10):2466-2470
CeO2-doped K0.5Na0.5NbO3 lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain
the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can
suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature
(T
C), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO2, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d
33 = 130 pC/N, planar electromechanical coupling coefficient k
p = 0.38, relative permittivity εr = 820, and loss tangent tanδ = 3%. 相似文献
7.
T. Joseph S. Uma J. Philip M. T. Sebastian 《Journal of Materials Science: Materials in Electronics》2011,22(8):1000-1009
A new polymer-ceramic composite was prepared using PTFE and low loss Sr2ZnSi2O7. The dielectric properties of the composite were studied in the microwave and radiofrequency ranges. The relative permittivity
(εr) and dielectric loss (tan δ) increased with the filler loading from 0.10 to 0.50 volume fractions (vf). The observed values of εr, thermal conductivity and coefficient of thermal expansion (CTE) were compared with the corresponding theoretical predictions.
The ability of the composite towards moisture absorption resistance was studied as a function of filler loading. It was also
found that the variation of εr was less than 2% in the temperature range 25–90 °C, at 1 MHz. For a filler content of 0.50 vf, the PTFE/Sr2ZnSi2O7 composite exhibited εr = 4.4, tan δ = 0.003 (at 4–6 GHz), CTE = 38.3 ppm/°C, thermal conductivity = 2.1 W/mK and moisture absorption = 0.09 wt%. 相似文献
8.
J.?S.?Almeida T.?S.?M.?Fernandes A.?J.?M.?Sales M.?A.?S.?Silva G.?F.?M.?P.?Júnior H.?O.?Rodrigues A.?S.?B.?Sombra
In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional
mixed oxide method and doped with 3, 5 and 10 wt. % Bi2O3–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the
triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of
dielectric permittivity (ε′
r
) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and BNO5Pb (5 wt. % PbO) with values ε′
r
~ 59.54 and ε′
r
~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with
values tan δ ~ 5.71 × 10−4 and tan δ ~ 2.19 × 10−4, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples,
obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′
r
~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at
temperature 80 °C, with about tan δ ~ 5.4 × 10−3. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C)
to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude
that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C,
which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H)
obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be
studied seeking the development ceramic capacitors for applications in radio frequency devices. 相似文献
9.
M. M. Nadoliisky M. P. Georgiev D. K. Nikolova V. A. Karadjova 《Journal of Materials Science: Materials in Electronics》2005,16(10):667-668
The article studies the dielectric properties, dc conductivity and ac conductivity of Be(IO3)2⋅4H2O single crystals. The dielectric constant ε has been defined for the three directions of the vectors a, b and c in the crystals in the temperature interval 280–340 K and frequency range 100 Hz–106 Hz. The crystals show strongly expressed anisotropy, at 20 ∘C and frequency 100 Hz εa = 235, εb = 30 and εc = 85. The frequency dependence of ε is evidence of the presence of low-frequency relaxation polarization in the crystals.
The activation energies of the three directions in the crystals have been derived from the temperature dependence of dc conductivity,
and they are 1.03 eV, 0.836 eV and 1.2 eV respectively. 相似文献
10.
A.c. measurements were preformed on bulk samples of Ca1−x
Sr
x
TiO3 (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 103–105 Hz . The experimental results indicate that the a.c. conductivity σa.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function
of frequency is well described by a power law Aω
S
with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal
dielectric response (UDR) behavior. 相似文献
11.
Polymer/Sr2ZnSi2O7 (SZS) ceramic composites suitable for substrate applications have been developed using the polymers polystyrene (PS), high
density polyethylene (HDPE) and Di-Glycidyl Ether of Bisphenol A (DGEBA). The dielectric, thermal and mechanical properties
of the composites are investigated as a function of various concentrations of the ceramic filler. The obtained values of relative
permittivity, dielectric loss tangent, thermal conductivity and coefficient of thermal expansion of the composites are compared
with the corresponding theoretical predictions. The relative permittivity of the polymer/ceramic composites increases with
filler loading. The dielectric loss tangent also shows the same trend except for DGEBA/SZS composites. The major advantages
of the ceramic loading are improvement in thermal conductivity and a decrease in the coefficient of thermal expansion. The
tensile strength of the composites decreases with increase in filler content, whereas an improvement is observed in microhardness.
The variation of relative permittivity (at 1 MHz) of the composites is also studied as a function of temperature. 相似文献
12.
Dongyun Guo Takashi Goto Chuanbin Wang Qiang Shen Lianmeng Zhang 《Journal of Materials Science: Materials in Electronics》2012,23(4):897-900
BaTi4O9 film was prepared on Pt/Ti/SiO2/Si substrate by laser chemical vapor deposition. The microstructure and dielectric properties were investigated. The single-phase
BaTi4O9 film with random orientation was obtained. The surface consisted of round and rectangular grains, and the cross-section was
columnar microstructure. The deposition rate (R
dep) was 135 μm h−1. The dielectric constant (ε
r) and loss (tanδ) were 35 and 0.01, respectively, at 1 MHz. With increasing temperature, ε
r increased and showed a broad peak around 736 K, which indicated there might be a phase transition. 相似文献
13.
Ba(Ti(0.9)Sn0.1)O3 (BTS) ceramic was prepared by a conventional ceramic processing. BTS-polycarbonate (PC) composites were prepared at different
BTS concentrations by weight in order to study their optical and dielectric properties. The absorption coefficient (α) was determined in the wavelength range from 250–600 nm at room temperature for all BTS-PC composites. The optical gap (E
opt) was also determined for BTS-PC composites. The variation of the absorption coefficient (α) and optical gap (E
opt) with BTS content are reported. It was found that BTS ceramic highly enhances the UV absorption of PC host at 300 nm. The
optical gap decreases up to the value of 3.93 eV as BTS content increases up to 35 wt% and this was attributed to the formation
of localized states in the forbidden gap. The relative dielectric permittivity, dielectric loss and loss tangent were measured
at temperature range from room temperature up to 150°C and at frequency values 1 kHz, 10 kHz and 50 kHz. Addition of BTS to
PC host, however, will increase relative dielectric permittivity, dielectric loss and loss tangent. Besides, increasing of
temperature will also increase relative dielectric permittivity, dielectric loss and loss tangent especially above the glass
transition temperature of PC host and this behaviour was attributed to the segmental motion of polymer chains. On the other
hand, this study shows that there is a good agreement between SEM, DSC and dielectric results and also between optical gap
and a.c. conductivity results. Moreover, SEM and DSC results reveal that addition of BTS ceramic particles to PC host will
reduce the physical bond between polymer chains or may be will increase the free volume in the polymer host and consequently
will enhance the segmental motion of polymer chains and this behaviour is independent of ceramic phase. 相似文献
14.
P. Ben-Ishai E. Sader Yu. Feldman I. Felner M. Weger 《Journal of Superconductivity and Novel Magnetism》2005,18(4):455-459
We present dielectric properties of ceramic anhydrous Na0.7CoO2 and the superconducting Na0.3CoO2·1.3H2O materials. The presence of water which induces superconductivity also may increase the dielectric constant (ε) of the hydrated material. This is consistent with the predicted relationship between the highε and the enhancement ofT
c in highT
c superconductors. The anhydrous sample is porous and the transport is due to some percolation via the pores. The porosity
is much higher for the hydrated material and the transport is ionic inside bulk water. 相似文献
15.
M. M. El-Nahass E. A. A. El-Shazly A. M. A. El-Barry H. S. S. Omar 《Journal of Materials Science》2011,46(17):5743-5750
Cadmium thiogallate CdGa2S4 thin films were prepared using a conventional thermal evaporation technique. The dark electrical resistivity calculations
were carried out at different elevated temperatures in the range 303–423 K and in thickness range 235–457 nm. The ac conductivity
and dielectric properties of CdGa2S4 film with thickness 457 nm has been studied as a function of temperature in the range from 303 to 383 K and in frequency
range from 174 Hz to 1.4 MHz. The experimental results indicate that σac(ω) is proportional to ω
s
and s ranges from 0.674 to 0.804. It was found that s increases by increasing temperature. The results obtained are discussed in terms of the non overlapping small polaron tunneling
model. The dielectric constant (ε′) and dielectric loss (ε″) were found to be decreased by increasing frequency and increased
by increasing temperature. The maximum barrier height (W
m) was estimated from the analysis of the dielectric loss (ε″) according to Giuntini’s equation. Its value for the as-deposited
films was found to be 0.294 eV. 相似文献
16.
《Materials Letters》2003,57(16-17):2545-2552
MX6Ti6O19 (M=Ba, Sr and Ca; X=Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (εr), loss tangent (tanδ) and temperature coefficient of dielectric constant (τεr) of the sintered ceramic compacts are studied using an impedance analyzer up to the 13-MHz region. The zinc compositions have relatively high dielectric constant and low loss tangent compared to the Mg analogue. Out of the samples studied, BaZn6Ti6O19 ceramics show excellent dielectric properties. The structure and microstructure of these ceramic samples are also studied using powder X-ray diffraction, FTIR and SEM methods, and the results are presented. 相似文献
17.
Kiran Singh Naresh Kumar Bharat Singh S. D. Kaushik N. K. Gaur Shovit Bhattacharya Sudhindra Rayaprol Charles Simon 《Journal of Superconductivity and Novel Magnetism》2011,24(6):1829-1838
Magnetic and dielectric properties of the double perovskite compounds of the type R
2CuTiO6 (RCTO, where R=Y, La, Pr and Nd) has been studied. Y2CuTiO6 (YCTO) crystallizes in a hexagonal unit cell, whereas the other three compounds form into orthorhombic structure. All four
compounds show paramagnetic behavior down to 5 K. The dielectric studies show moderate dielectric constant (ε′) and very small dielectric loss (tan δ) for YCTO. The orthorhombic members of RCTO compounds exhibit moderate values of ε′ and tan δ. The dielectric properties are presented and discussed here in the light of the influence of structure and rare-earth ions
on the physical properties of RCTO compounds. 相似文献
18.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
19.
The effects of CuO–Bi2O3–V2O5 additions on the sintering temperature and the microwave dielectric properties of MgTiO3 ceramics were investigated systematically. The CuO–Bi2O3–V2O5 (CuBiV) addition significantly lowered the densification temperature of MgTiO3 ceramics from 1400 °C to about 900 °C, which is due to the formation of the liquid-phase of BiVO4 and Cu3(VO4)2 during sintering. The saturated dielectric constant (εr) increased, the maximum quality factor (Qf) values decreased and the temperature coefficient of resonant frequency (τf) shifted to a negative value with the increasing CuBiV content, which is mainly attributed to the increase of the second
phase BiVO4. MgTiO3 ceramics with 6 wt.% CuBiV addition sintered at 900 °C for 2 h have the excellent microwave dielectric properties: ε r= 18.1, Qf = 20300 GHz and τf = −57 ppm/ °C. 相似文献
20.
GUO-HUA CHEN JIN LIU XU-QIONG LI HUA-RUI XU MIN-HONG JIANG CHANG-RONG ZHOU 《Bulletin of Materials Science》2011,34(6):1233-1236
Phase purity, microstructure, sinterability and microwave dielectric properties of BaCu(B2O5)-added Li2ZnTi3O8 ceramics and their cofireability with Ag electrode were investigated. A small amount of BaCu (B2O5) can effectively reduce the sintering temperature from 1075°C to 925°C, and it does not induce much degradation of the microwave
dielectric properties. Microwave dielectric properties of ε
r = 23·1, Q × f = 22,732 GHz and τ
f = − 17·6 ppm/°C were obtained for Li2ZnTi3O8 ceramic with 1·5 wt% BaCu(B2O5) sintered at 925°C for 4 h. The Li2ZnTi3O8 +BCB ceramics can be compatible with Ag electrode, which makes it a promising microwave dielectric material for low-temperature
co-fired ceramic technology application. 相似文献